1. Field of the Invention
The present invention relates to a composition for stabilizing biological cultures in brine solutions under anaerobic/anoxic conditions and to a process for treating brine solutions biologically under anaerobic/anoxic conditions, where the cultures include one or a plurality of microorganisms capable degrading a desired pollutant in a brine solution.
More particularly, the present invention relates to a composition for stabilizing a biological culture in a brine solution under anaerobic/anoxic conditions, where the composition includes an effective amount of a divalent cation, where the effective amount of the divalent cation is sufficient to produce a divalent/monovalent cation ratio in the brine solution of at least a 0.05 mole/mole or a divalent/monovalent cation ratio greater than or equal to 0.05 mole/mole, where the ratio promotes growth and sustained proliferation of biological microorganisms capable of degrading pollutants or decreasing a concentration of pollutants in the brine solution. The present invention relates to a method using the composition to treat contaminated brine solutions under anaerobic/anoxic conditions. In one preferred embodiment, the stabilized brine solutions are geared to stably grow perchlorate degrading microorganism. In another preferred embodiment, the stabilized brine solutions are geared to stably grow perchlorate and nitrate degrading microorganisms.
2. Description of the Related Art
Many industrial wastes stream are composed of aqueous salt solutions such as ion-exchange brines, oilfield production brines, spent caustic solution, and brines produced during chemical processes that contain elevated levels or concentrations of salts such as Na+. These waste stream may also contain contaminants that would be amenable to biological treatment, microbial treatment, if organisms or microbes could function in high salt waste streams. Some have noted that there is an increasing need for a biological treatment adapted to saline and alkaline environments in industrial wastewater management and that traditional pollutant biodegradation is less efficient or does not function when a salinity of the stream or solution increases above the salinity of seawater.
Alva and Peyton (2003) examined biological culture growth and phenol degradation at different salt concentrations, but they did not increase the concentration of divalent cations when they increased the Na+ concentration. Thus, the divalent to monovalent ratio decreased during the study.
Logan et al. (2001b) screened six sources of inoculum collected from different saltwater environments for perchlorate reduction. After three months incubation, growth was observed in media containing perchlorate and 3% NaCl with inocula from only three sources (seawater, saline lake water and biofilm/sludge). Two of these three (seawater and saline lake water) grew through 3% to 7% salinity in subsequent transfers. They make no mention of increasing the divalent cation concentrations when they increased the Na+ concentrations in their tests.
In U.S. Pat. No. 6,077,432 a method for the treatment of wastewater, suspected of being contaminated with perchlorates, nitrates, hydrolysates and other energetic materials is disclosed. The method comprises (a) providing at least one microaerobic reactor containing a mixed bacterial culture capable of reducing perchlorate, nitrate, hydrolysates and other energetic products; (b) feeding contaminated wastewater into the microaerobic reactor; (c) maintaining a microaerobic environment in the microaerobic reactor by at least one method selected from the group consisting of (i) mixing air and nitrogen gas and sparging or purging the reactor with the gas mixture; (ii) using a nitrogen membrane separator to provide a low oxygen-containing nitrogen gas to the reactor for sparging or purging; (iii) adding air to the reactor for sparging or purging as necessary to maintain a target dissolved oxygen concentration or a target oxygen concentration in head space gas present in the reactor; and (iv) adding and/or maintaining oxygenated ions and/or oxygenated molecules; and (d) maintaining suitable nutrient and environmental conditions in the microaerobic reactor so as to cause decontamination of the contaminated wastewater.
Okeke et al. (2002) obtained cultures that could reduce both perchlorate and nitrate in 0 to 5% NaCl environments, but no effort was made to adjust the divalent cation to monovalent cation ratio.
Clifford and Liu (1993) developed a sequencing-batch-reactor (SBR) denitrification process to treat and reuse nitrate brine containing 3% NaCl. A pilot study using this ion-exchange process with batch biological denitrification and reuse of the spent brine was conducted successfully in McFarland, Calif. in 1994 where spent brine was denitrified and reused 38 times. (Liu and Clifford, 1996). Compared with a conventional ion-exchange process, brine denitrification and reuse reduced the salt consumption by 50 percent and waste discharge by more than 90 percent.
Microbial perchlorate reduction under anaerobic conditions has been studied by many researchers. See for example Attaway and Smith, 1993; Herman and Frankenberger, 1999; Logan et al., 2001a; Rikken et al., 1996. Many microorganisms can reduce perchlorate to harmless chloride. Unfortunately, most known perchlorate-reducing microorganisms cannot endure high salinity in the growth media, and usually require less than 2% to 3% NaCl. See for example Coates et al. (2000), Malmqvist et al. (1994), and Michaelidou et al. (2000).
Several other researchers have conducted salt tolerance tests for the growth of many organisms, but none that changed the divalent cation concentration when the sodium concentration was changed.
Thus, there is a need in the art for a brine solution capable of stable microbial growth under anaerobic/anoxic conditions and a method to stabilize biological treatment systems in high saline or brine solutions under anaerobic/anoxic conditions.